A cam follower is a machine element which rolls along a track, or in a groove, to provide guided movement to a device to which it is connected. One type of cam follower is a wheel which is rotatable on a shaft, the wheel and shaft forming a type of bearing on which the surfaces slide relative to each other, without balls or rollers between the surfaces. A bearing is a machine element which reduces friction between fixed and moving parts, and may be a ball bearing, roller bearing or bushing bearing. A bushing is a tubular metal lining used to reduce friction.
A standard, commercially available cam follower consists of thread shaft, roller or needle bearing and an outer race (cam track). The outer race (raceway). typically rolls on the cam (cam track).
To provide smooth rotation and to prevent ceasing of the bearing the cam follower is lubricated. For this purpose the threaded shaft has a bore, through the shaft, which connects the bearing chamber with an outside grease fitting. Lubrication can be provided manually, with grease being pressed into the bearing at regular intervals, or a central lubricating system, which may be automated, may apply grease, under pressure, at regular intervals.
In many instances the central lubricating system is designed and built for the single purpose of lubricating the cam followers. It is especially costly to build and maintain lubricating systems to lubricate multiple cam followers rotating around a stationary cam.
While providing the necessary lubrication to the cam follower rollers, central lubrication can fail. For example, grease may build up in the supply tube. Without lubrication, the cam follower will cease to rotate causing damage to the cam and possibly causing follow-up damage and costly unplanned down-time.
Over-greasing causes a different problem. Excessive grease may cause the outer ring of the cam follower to develop resistance to rotation causing partial sliding of the roller race on the cam. High friction develops at the point of contact between cam follower and the cam as the cam follower is "dragged along" without rotation. The cam follower race can develop a flat which makes it dysfunctional and causing excessive wear on the cam. Cam replacement is usually very costly since it requires several days of down-time.
Many processing machines require the use of cam followers. A cam follower typically rides on a cam, or in a groove representing a cam. The shape of the cam, or groove, determines the ultimate trajectory of the machine component to which the cam follower is attached, e.g. a sawing head being guided along the edge of a shoe sole. Cam followers can also transmit a considerable radial force.
An especially important application of the non-lubricated cam followers of the present invention is in metal can production machinery.
Metal cans are often produced as "two piece cans" which consist of a cylindrical can body with an integral bottom wall and a can top. Millions of such cans are made each day. They are generally made of thin aluminum or steel sheet metal. For example, aluminum cans are used to pack gas pressurized liquids, such as beer and soda. The can must have a certain strength so that it can withstand internal gas pressure as well as the pressures from stacking, dispensing machines and handling. However, thickness of the sheet metal is an important part of the cost of such cans. If the metal may be made thinner, while retaining the required strength, then the cans may be produced at a decreased cost.
One way to obtain can strength, using sheet metal, is to form circular curves in the can bottom. Such curves, viewed from the bottom of the can, are one or more concentric circles in the can bottom and/or can side wall near the bottom. Seen in cross-section such curves are rounded, generally in a hemispherical shape.
The can making machine which forms the shape of the can body is sometimes called a "necker". It operates by applying pressure to the can body after it has been formed into its general body shape, e.g., a cylinder or multi-angular shape with an integral bottom wall.
The necker is a type of tool and die in which the sheet metal is placed between the tool, having a protrusion, and the die, having a matching indentation. The tool and die are brought together, under pressure forcing the sheet metal to assume the shape of the protrusion-indentation.
Cans are produced at high speed, for example, at the speed of up to 2500 cans per minute. The can bodies are squeezed ("necked") between opposite moving ram assemblies.
In such can making necker machinery, the cam follower usually rides on a stationary cam with the rotational axis parallel to the cam's surface. The cam followers are riding on the cam's surface, one on each side of the cam, at the same time they are rotating around the cam's axis on a 14" radius. The cam followers are mounted on pushers (rams) which are moved back and forth, by their attached cam followers, in an accelerating and decelerating movement following the cam's profile. Considerable radial force is developed on the cam follower during the can necking (extrusion) operation.
Lubrication to the cam followers is provided through a central lubrication system. This system requires a rotational coupling as the cam followers are carried around the machine axis. The seals in the rotational couplings are subject to wear and the coupling over time will often leak grease.
Grease lubrication, manual or central, is a burden. Before any adjustments to the machine set-up can be made, grease has first to be cleaned from the parts. The added clean-up time burden is felt most during emergency stops. When grease reaches the final product, it has to be rejected. The grease, which must be FDA approved as being edible, is expensive.
In U.S. Pat. No. 5,467,628, assigned to Belvac Production Machinery, incorporated by reference, a sliding bushing 20 surrounds a ram 22 in a can bottom reprofiler machine. The tail end of the ram carries cam follower wheels 56 which rides against a cam track 57. This general type of double-ram can forming machine is also shown in U.S. Pat. Nos. 4,732,027 and 4,272,977.
In U.S. Pat. No. 5,368,398 a diamond bearing assembly includes opposite thrust bearing rings. In U.S. Pat. No. 4,468,138 a polycrystalline diamond insert is used in the thrust roller bearing of a Turbodrill. U.S. Pat. No. 4,708,496 shows a thrust roller bearing for oil well downhole drilling. U.S. Pat. No. 5,254,141 relates to adhering a diamond coating to a substrate. The above-mentioned patents are incorporated by reference.